The present invention refers generally to structures for absorbent articles and to absorbent articles as, for example, disposable napkins and diapers and, more specifically, to an absorbent article structure and to articles manufactured with such structure, wherein the outer, impervious layer of the structure and articles is made of an inherently-porous paper substrate impregnated with a selective adhesive which only adheres to itself, so that the structure and the articles become impervious to liquids and permeable to air, the articles -- as for example disposable diapers -- eliminating the use of safety pins, buttons, tapes and tabs for their closure on the wearer's body.
The current technique in the manufacture of absorbent structures -- as, for example, diapers or surgical sheets -- is based on the use of three basic layers of material: an internal, permeable layer, usually made of a non-woven cellulosic fabric or of a highly-porous and absorbent paper; an intermediate layer, of a highly absorbent material, usually made of a loosely-compacted fibrous material; and an outer layer, impervious to liquids, usually made of a plastic material.
Such structures have been known for a long time, and impervious outer layers, made, for example, of a thoroughly impervious material -- as rubber and several types of plastics -- with the layers being able to be an integral part of the structure or detachable from other layers, are current in the patent literature since the beginning of this century.
It so happens that all such structures, especially when shaped as diapers, produce a so-called "greenhouse" effect, causing great discomfort to the wearer. Attempts to overcome the problems caused by the greenhouse effect, with the provision of microscopic perforations and tubes with capillary action, preventing the migration of liquid and enabling breathing of the diaper, are disclosed in recent but the difficulties of accurate manufacture of such structures with the extremely high rates desired in the manufacture of absorbent articles produce certain disadvantages in such types of structure.
The widespread use of plastics as the impervious outer layer contributes substantially to the problem known as the "greenhouse" effect. The use of plasticized paper, as in U.S. Pat. No. 2,627,858, (1950), does not contribute to a solution, since the impregnation of paper with polystyrene on its surface renders the outer layer impervious both to liquid and air.
In the absorbent articles where a portion of the articles should be adhered to another portion for the formation of a garment, as in diapers, a countless number of fastening devices has been proposed in the prior art, from the traditional safety pins, common or pressure buttons, hooks, tapes capable of forming knots, with the fastening devices most widespread now being adhesive tapes. Usually, the adhesive tapes are attached to or fastened on the impervious outer layer of the diaper, having an adhesive surface which remains folded over and protected until the moment of its use. In some cases, as in U.S. Pat. No. 2,649,858, (1951), U.S. Pat. No. 3,620,217, (1970), U.S. Pat. No. 3,901,237, (1974) or in U.S. Pat. No. 2,290,110, (1941), adhesive areas are provided in certain zones of the diaper, which remain duly protected until the moment of use. In other cases, as in U.S. Pat. No. 4,055,181, (1976), and U.S. Pat. No. 4,034,752, (1976), the tapes are "built in" the diaper and do not protrude outwardly. Some of the above-mentioned patents enable, in one way or another, the adjustment or reutilization of the diaper, and the fastening device can be opened and closed again.
The drawback of the fastening devices used until now lies in the fact that their manufacture and installation in the diapers are laborious and expensive steps which complicate the manufacturing process, which process should be necessarily fast and simple in order that a disposable diaper reaches the market with a reasonable cost.
One advantage of the present invention is the provision of a structure in which the outer layer is impervious to liquid and permeable to air, eliminating the "greenhouse" effect on articles made with this structure. Also the need for separate fastening means is eliminated. The closure of the present invention can be opened and resealed repeatedly. Furthermore, the entire product can be made without the use of non-breathable plastic materials.
These and other objects of the invention can be better understood by reading the following detailed description and the accompanying drawings.